Anatomy of a 300 Myr old fjord in Namibia
- Author(s)
- D. P. Le Heron, R. Wohlschlägl, P. Mejías Osorio, C. Kettler, A. Nduutepo
- Abstract
Namibia is remarkable in terms of its network of c. 300 Myr old fjords, cut by Gondwanan glaciers at high palaeolatitudes during the Late Paleozoic Ice Age (LPIA). A classic suite of structures is preserved on Proterozoic bedrock, including striations, roches moutonnées and other subglacial features within many of these palaeovalleys. Some palaeovalleys are plastered with comparatively thin diamictites (a few metres) of presumed subglacial origin, in turn capped by ice marginal delta successions (tens of metres). Close examination of deposits in the outer Orutanda Fjord palaeovalley reveals an architecture that shows departure from this trend. There, boulder-bearing diamictites pass laterally into highly contorted heterolithic successions comprising folded and faulted sandstones, siltstones and shales. Aerial imagery from uncrewed aerial vehicles in tandem with traditional field observations permits mapping of assemblages of soft-sediment deformation structures (tight to recumbent folds, deformation bands, faults, sheath folds) together with spatial mapping of the long axis of boulders in diamictite. Collectively, this assemblage of structures points towards subglacial deformation, and hence an origin as a ‘deforming bed’ beneath a glacier. Although several open questions remain regarding the precise deformation mechanisms, the concept of glacial readvances into a deeply incised palaeovalley is proposed, by direct analogy to similar stratigraphic architectures in the LPIA record of South America.
- Organisation(s)
- Department of Geology
- External organisation(s)
- ZAMG, Ministry for Mines and Energy
- Journal
- Journal of the Geological Society
- Volume
- 182
- ISSN
- 0016-7649
- DOI
- https://doi.org/10.1144/jgs2024-074
- Publication date
- 01-2025
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105121 Sedimentology
- ASJC Scopus subject areas
- Geology
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/b35695ea-2727-4675-8fe4-e30511227578